With the current NotBorderNear-system, it's difficult to make a biome being a border next to only three of your biomes and not next to your hundred other ones. In some cases, having a setting such as OnlyBorderNear, would be much easier.
OnlyBorderNear: Extreme Hills, Extreme Hills+
That's easier than
NotBorderNear: insert all your biomes which are not Extreme Hills or Extreme Hills+ here
(it's easier especially when one biome has many borders, such as the ocean. Cold Beach next to cold biomes, Beach next to temperate ones, Stone Beach next to mountainous ones, and then I'd like to add some others such as Gravel Beach or Cliff. Whoops. Difficulties appear.)
What's very important, is that OnlyBorderNear should not replace NotBorderNear. There should be a choice between the two, so you should be able to choose per worldconfig.ini between NotBorderNear and OnlyBorderNear. The suggested setting is actually the opposite of the already existing setting.